Measurement and Modeling of the Role of Face Protections in the Airborne Transmission of SARS-CoV-2 with Focus on Mask Leakage and Development of a Wearable Air Quality Sensor

Abstract

Facemasks have gained a considerable news coverage during the SARS-CoV-2 outbreak. The use of facemasks by the general public was initially controversial as interrogations remained regarding the airborne transmission of the disease, and the ability of masks to reduce the risk of infection was under scrutiny. However, masks rapidly proved to be one of the best options to curb the spread of the COVID-19, together with distanciation measures and hand disinfection. Governments and health authorities soon recommended or imposed the generalized use of masks, with variations over time to adapt to the different infection waves, and with significant differences between countries. Both insufficient production and stockpiling at the beginning of the pandemic resulted in shortages of personal protective equipment, especially in hospitals, and fueled the development of community masks based on alternative materials (textiles, such as cotton) as a complement to already existing filtering face pieces (FFP) and medical masks (also known as surgical masks). The measurement of the filtration efficiency of various materials intended to be used in facemasks has been widely documented. However, another crucial aspect of the masks’ protection, the leaking flow, has often been neglected in models estimating the impact of masks on the infection risk and on the spread of the disease. This thesis investigates the mechanisms of the protection provided by facemasks with a strong focus on the leakages. To that extend, an extensive literature review was conducted, measurements on full-face masks were completed, and a computational model was developed to integrate leakage in the calculation of the infection risk. The thesis also presents a potential innovation contributing to the development of smarter masks intended to inform the wearer about the air quality. An alternative full-face personal protective device based on a commercial snorkeling mask featuring a 3D-printed adapter to fit two medical-grade filters was presented; and its level of respiratory protection was investigated. The filtration efficiency and pressure drop of several filters regularly used in medical facilities for patient ventilation were measured. Investigations on the full-face mask featuring high-efficiency filters highlighted the impact on the respiratory protection of faceseal leakage and its variability. The developed device provided a level of respiratory protection equivalent to a FFP2 mask and could be reused as it did not suffer from a degradation of its protection efficiency upon disinfection. A computational model was developed to investigate the role of the leaking flow in the ability of masks to offer adequate levels of respiratory protection and source control against SARS- CoV-2. The model is composed of several modules describing the fate of respiratory particles from their emission by an infected individual to their inhalation by a susceptible person, considering their filtration by the emitter’s and the receiver’s facemasks including leakage, their spread and accumulation around the emitter considering local turbulences, and their deposition in the receiver’s respiratory system upon inhalation. The model was applied to compare various types of masks to analyze the efficiency of source control versus respiratory protection, and to assess the impact of different leakage scenarios including a degraded fit for filtering face pieces. The investigations showed that the leaking flow is the main source of particles entering a mask and being released from a mask. Moreover, a degraded fit on a FFP2 mask can offer less protection than a well-fitted surgical or community mask. An updated version of the computational model allowed the calculation of the infection risk in different settings, to compare the impact of leakage and vaccination considering the emergence of new variants of SARS-CoV-2. An extensive literature review provided realistic data on leakage which were integrated into the model. The investigations pointed out the importance to adapt the sizes of the masks to the facial features and dimensions of the wearers to limit the leakage and improve the protection. A widespread and adapted use of facemasks combined with a high vaccination rate was found to be critical to tackle more infectious SARS-CoV-2 variants. Finally, a potential innovation for future smart facemasks was investigated, consisting of a 3D- printed sensor prototype for the monitoring of volatile organic compounds. The sensor was based on ionic liquids and showed a reversible and concentration-dependent change of resistive properties upon exposure to various concentrations of polar organic solvents. The compact and energy-efficient sensor has the potential of being integrated into a facemask to monitor the air quality around the wearer.